The usual forms of assembled units are of two types as far as the rims are concerned. They are made either with so-called well-base rims, possessing tapering seats inclined relative to the axis of rotation of the unit at an angle of 5° or 15°, or with flat or practically flat-base rims having seats inclined at either 0° or 5° relative to the axis of rotation.
So-called well-base rims comprise a mounting groove whose diameter is significantly less than the nominal diameter of the rim. This internal diameter of the rim can be considered by users to be too small because it does not allow the use for example of brake drums of dimensions suitable for effective braking of the vehicles, which are increasingly powerful for their weight.
As a result, these rims are often used for assembled units intended for passenger and/or heavy vehicles, but are used much less and sometimes not at all for the other types of vehicles, such as for example building site and civil engineering machines.
To make an assembled unit, particularly of “tubeless” type, a flat-base rim requires the presence of at least one detachable lateral ring, a locking ring and a seal, and obviously the presence of the wheel rim having a fixed lip on the opposite side to that where the parts are detachable. The reason for this is that the vehicle wheel dimensions and tire dimensions and in particular the stiffness of the lower regions are such that said wheels must be made in several parts to enable the tire to be mounted on a rim. At least three parts are therefore required. In most cases the number of parts required is more than three and can sometimes be as many as six parts for tires of large dimensions, without counting the parts necessary for mounting the wheels on the vehicle. Except for the rubber seals, the parts of a rim are metallic, and therefore heavy, large, and difficult to handle. It follows that the mounting and removing of large and very large tires are difficult and time-consuming operations. The fitting and/or removal of a wheel equipped with such a tire requires immobilising the vehicle or machine for a not insignificant length of time, which is thus detrimental to the productivity desired when using these vehicles.
Patent Application WO 00/71365 disclosed a technique that simplifies the mounting of tires, which are mounted directly on the hub, the hub thus acting as the rim. Independent mounting rings act as rim seats and are held in place by locking rings which are secured to the hub typically by means of mating profiles. In this technique, the locking ring consists of a cured rubber compound reinforced by and coating a reinforcing ring that is circumferentially elastic and radially resistant to compression.
Such a technique is very promising because it eliminates the stages of mounting on a rim and fixing a wheel to the vehicle, since the tires are mounted directly on the hub by means of the mounting rings and locking rings. Moreover, since the number of components is greatly reduced, maintenance of these components is simplified.
However, whether this latter technique is used or whether the tires are connected to wheels consisting of a plurality of parts, when it comes to changing a tire or switching two tires on the vehicle, either the wheel, or the tire, or both, still have to be removed. This involves deflating the tire, which is essential when changing a tire and practically essential at least in part when switching assembled units in order to reduce their weight.
The deflation time for a 59/80R63 size tire fitted to a dumper-type vehicle is more than 30 minutes. This means that a complete switching of the tires of a vehicle requires a total deflation time of at least two hours.
Given the fact that in a mine a work cycle corresponding to transporting one full skip of a dumper-type vehicle is usually less than this 30-minute period, it is obvious that time spent working on the tires has a direct and substantial influence on the productivity of the vehicles.
There is therefore a desire to reduce the deflation time of such tires.
Tires for civil engineering machines, such as the vehicles used in mines of dumper-type for example, are usually pumped to a pressure of between 4 and 10 bar for ordinary loads and sizes.
Current deflation techniques involve releasing the inner part of the inflation valve to let the air escape. The deflation time could be reduced by increasing the size of current inflation valve systems, but their design would become difficult and the escape of air occasioned by the pressures and volume of air in this type of tire would put the operator, who has to release the inner part of the valve, in danger.
Existing valves of butterfly, plug or open/close element type with suitable dimensions have been envisaged but they have various drawbacks. In the first place, they are too large to be fitted to some vehicles, and secondly the maintenance of these valves requires stripping them completely. Maintenance must be taken into account because when the air escapes from the assembled unit, it carries with it particles such as residues of corrosion from the wheel, fragments of tire, if the latter has suffered deterioration, and liquids resulting from condensation and specific products designed to prevent corrosion.